The measurement of airway humidity is reviewed, particularly the methods which have been used during anaesthesia and endotracheal intubation. Reported heat and moisture patterns are related to possible effects on the tracheal mucosa and whole body heat balance. Mucosal dysfunction and hypothermia are more likely when dry gases are inhaled from a non-rebreathing system. Even with high fresh-gas inflow, the circle absorber system appears to present an inspiratory moisture content which is comparable to that found during mouth breathing.
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